Communication networks often include a multiplicity of interconnected switching nodes. Each switching node has a number of input ports and a number of output ports. A call represents a communication session taking place between two or more end nodes over a connection formed along a path through various switching nodes. A call arriving at an input port of each switching node in the call's path is switched through the switching node to a selected output port. Typically, communications for many independent calls are multiplexed together for combined transmission between the switching nodes over communication links. Accordingly, a new call can be connected through the network so long as sufficient residual capacity exists over communication links through the network of switching nodes.
In conventional networks, the topology of communication links between switching nodes changes slowly. For example, a new communication link is brought on-line infrequently. Once brought on-line, a new link becomes available for routing calls and typically remains on-line for a significant period of time. However, an existing link may go out of service due to a failure or other unusual event. When the topology of the network is reasonably static, a conventional call routing process is typically programmed to consider available link capacities in making call admission decisions. Hence, a conventional call routing process simply attempts to admit as many new connections as possible, subject to the capacity constraints of links in the relatively static topology. However, if sufficient resources are not available at the time of a connection request, the request is blocked. A blocked request is an undesirable event because denial of communication services results in unsatisfied customers and a potential loss of revenue.
When a communication network relies upon switching nodes located in satellites orbiting the earth, the topology of communication links can be more dynamic. In other words, the presence or absence of communication links between the switching nodes can change on a moment by moment basis. Topologies may change, for example, due to movements of satellite switching nodes located in non-geosynchronous orbits.
In addition, topologies may desirably change to provide flexibility in allocating network resources to call traffic demands. The ability to flexibly allocate space-based resources leads to increasingly better utilization of the resources. Fewer resources can then be placed in the satellites to accommodate a given amount of network call traffic, leading to a great cost savings. Unfortunately, a dynamic topology of switching links greatly increases the demands on a call routing process and conventional call routing processes achieve unsuitable results.
Accordingly, a need exists for a communications network in which the communication link topology itself is configured in response to demands for communication resources and calls are efficiently routed.